“I just wanted to play Portal…”

Prologue

A friend on Facebook mentioned that he wanted to play some games on his Mac to help with an inner ear problem (practicing with virtual motion apparently helps with vertigo from real motion) — I had suggested Portal, as that’s a very changing-viewpoint-intensive game. Unfortunately, neither of us knew that Portal and Portal 2 are both 32-bit apps, and so they don’t run under more modern Mac OS X’s — anything past Mojave dropped 32-bit support. I said, “I’m sure there’s a way I could make this work.”

Hubris.

They don’t call it Boot Camp for nothing

My initial thought was, well, of course most games run best under Windows; why don’t I set up Boot Camp on this machine? I’ve always wanted to see if it would work.

Well, it might. But the machine I have to play around with — a 2011 MacBook Pro, the last one to have user-upgradable memory and disk — does not play well with modern versions of Boot Camp. See, modern versions of Boot Camp assume that you’ll be able to build a Windows installer USB stick and boot off that to install Windows. Boot Camp does build the installer USB stick; it’s just that my 2011 MBP can’t boot anything except OS X from USB. It could install from DVD, but a) I had no DVD blanks on hand and b) newer Boot Camp does not believe in DVD drives. There’s no option to tell it “please burn this to DVD”.

I started exploring other options, trying to find one I wouldn’t feel like an utter heel trying to convince a not-so-technical friend to use, and there just wasn’t one. The closest I got was building a Windows VM, but that started getting messy and I decided if this was going to work, it needed to work with the tools that a typical Mac user would have, and shouldn’t require the installer to understand how to mount ISOs on virtual machines, and worse.

Dual-wielding Mac OS installs

My MPB can run 32-bit OSes, so I decided that the simplest possible option was create a second partition on the internal HD and install Mojave (the last 32-bit OS X) on it. This was a less complex option by far; the worst it required was a little work in Disk Utility to create the target partition, and issuing one command in Terminal.app to create the installer USB (which yes, my MBP would boot, since it was OS X).

This article was really helpful in getting it done; I won’t repeat the whole thing here, but just mention the highlights:

• Modern Mac OSes use APFS, and creating an extra APFS volume in free space on the internal drive only took a couple minutes.
• Links to older version of OS X are available through this Apple support page; because Apple does get rid of older OSes, I recommend getting the installer you want and backing it up in case you ever want it again. Currently (as of May 2021), you can get Catalina, Mojave (the last 32-bit OS X), and High Sierra as installer apps from the App Store, and Sierra, El Capitan, and Yosemite as .dmg files, which install the installer. Older versions are probably available out there on the Internet, but they won’t be official Apple source.
• Creating the installer is the one more-sophisticated step, in that it requires you to enter a command in Terminal.app to create the USB stick. That’s documented in this Apple support document; it’s only one command, so it’s not too scary.
• Once you have a usable USB stick, it’s relatively straightforward. Boot the machine while holding down the Option key, and you’ll get a menu of disks to boot from. Pick the installer USB. You go through a couple screens to get to the install disk; pick the APFS partition you added.

The result

That’s pretty much it; wait for the installer to do its thing. One it’s finished, you’ll be up in Mojave. If your Catalina or Big Sur install is on an encrypted disk, you’ll get a prompt to enter your userID password from the other install; note that there are two partitions it will have to unlock. The first will use a bizarre dashed-hexidecimal username; if you’ve got more than one user, you’ll have to try combinations of different weird usernames and your login password until it unlocks. The second will use your regular username. (You can have Mojave remember these so you won’t have to enter them again.)

And now you’re up on Mojave! Note that since your Catalina/Big Sur install is readable, you can run applications that are installed on that system in this one without reinstalling them. In this case we want to run Steam, which runs just fine and allows you to install Portal to the Mojave partition and run it there.

This still isn’t as simple as having an OS that supports both 32 and 64 bit apps, but it will work. If you’ve got 32-bit apps you really need to keep, then this is a way to have the best of both: the newest OS and one that still runs all the things you need.